Re: cellular phones

[John Denker <jsd@MONMOUTH.COM>]

At 03:22 PM 5/27/00 -0400, Ludwik Kowalski wrote:
> There was a TV program about the brain cancer
> danger from cell phones last night. They said that
> the measured dose rates (of electromatgetic radiation
> absorbed in the head tissue) from common cell
> phones exceeds the FCC recommended limit of
> 1.6 W/kg.
>
> I am puzzled.

...as well you should be.

Let's see.  My phone has a rated Tx power of 600 mW MAX at a frequency of
840 MHz or so.  A typical human brain is about 1 liter, 1 kg.  Starting
there, we can do some physics.

Suppose half the Tx power gets absorbed by the brain.  Then in round
numbers we have 0.3 W/kg, MAX, under conservative assumptions.

To put this in perspective, note that the normal metabolism of the human
brain is about 50 W.

It's hard to believe that 0.1% extra heat load is a health risk.  (Persons
with brains the size of a walnut might have a problem :-).

Note that one cannot be confident that the waves "just go right through",
nor can one be confident that the waves are all stopped in the scalp before
they reach the brain.  See
  http://www.deas.harvard.edu/courses/es151/pages/gallery/images/water_spec
http://www.deas.harvard.edu/courses/es151/pages/gallery/images/water_spec.html
for an online version of Jackson's famous graph of EM absorption versus
frequency.

=====================

There's a story going around about one of the first guys who sued his
cellular provider, alleging that his phone gave him brain cancer.  He put
on an "expert" who had detailed argument about microwave heating of the
brain tissue, increased cell division rates, et cetera.  Later, the defense
pointed out that the plaintiff habitually wore a hat.  Even the plaintiff's
expert had to concede that the hat heated his brain far more than the phone
did.

At 04:10 PM 5/27/00 -0400, John Cooper wrote:
>   On the other hand, the incidence of bilateral
> cataracts among aircraft radar repairmen during
> and after WWII resulted from the back of their
> cornea's being essentially microwaved by accidental
> exposure to the beam.

Right.  Aircraft radars can put out thousands of watts;  ground radars can
put out millions of watts.  Corneas have no blood vessels, so they are
exceptionally vulnerable to microwave heating, especially above 10GHz.

A level-headed discussion of RF safety thresholds, and further references,
can be found at
  http://www.ce.umist.ac.uk/Department/SafMan2_32.asp